I think it's pretty clear that Thanos was/is still after the Cosmic Cube. Maybe he doesn't want to try and take the Infinity Gauntlet from Odin yet. Thanos is waiting for the perfect time to put all of the events of his plan in motion . As we saw in Marvel's The Avengers, he wasn't exactly expecting resistance. But that doesn't mean that he's any less excited about the prospect of taking on the Avengers.

The last we saw of the Cosmic Cube it was being taken to Asgard. Maybe at the end of Thor: The Dark World we see someone or something stealing the Tesseract and then realizing that the Infinity Gauntlet is in the vault as well. Odin is getting older, Thor is probably in the process of becoming the King of Asgard and the Destroyer is gone. Loki has served his purpose. Asgard will be as weak as ever in Thor: The Dark World.

Or, picture this. Post-credit scene of Thor: The Dark World we see a figure in the dark or Odin's vault. He's stumbling around maybe knocking stuff over. He walks up to the Cosmic Cube, we still haven't seen his face yet. Then we see him walk up to the Infinity Gauntlet. The light hits his face and guess who we see? It's Star-Lord! Just an idea.